Thyroid and Weight Gain: What’s Normal?

Unexplained weight gain, especially in women age 60 and over, is one of the most common signs of a thyroid disorder called hypothyroidism, according to the American Thyroid Association (ATA).

The thyroid gland is a butterfly-shaped endocrine gland that is found in the lower front of the neck. It lies just below the Adam’s apple, and along the front of the windpipe.

This gland produces thyroid hormones that are secreted into the blood, which are then transmitted to every tissue in the body. These important hormones help maintain body heat, as well as keep the brain, heart, muscles, and other organs working effectively.

Hypothyroidism occurs when the thyroid gland is underactive or does not produce enough hormones to properly regulate the body. This condition can have a real impact on mood and energy levels. In fact, hypothyroidism tends to make people feel sluggish, tired, and even depressed.

It can also lead to unexplained, and often unwanted, weight gain.

To determine hormone levels, a doctor (usually an endocrinologist) performs a simple blood test that measures thyroid stimulating hormone (TSH). If TSH levels are too high, this is a strong indicator that hormone production levels are too low, which generally leads to a diagnosis of hypothyroidism. When the opposite occurs, too little TSH is detected because too many hormones are already flooding the body’s systems. This, in turn, is called hyperthyroidism.

So, how much weight do people with hypothyroidism typically gain before and after diagnosis and treatment?

According to one study conducted by researchers at the National Heart, Lung, and Blood Institute’s Framington Heart Study, small increases in TSH levels led women to gain an average of 5 pounds over the study’s three-and-a-half-year follow-up period. Men, on average, gained less, adding 3 pounds during this same timeframe.

Most of the extra weight gained in hypothyroid individuals is due to excess accumulation of salt and water, according to the ATA. Massive weight gain is rarely associated with this condition. Once treatment for hypothyroidism is introduced, a small weight loss can be expected—usually less than 10 percent of body weight.

However, hypothyroidism generally develops gradually, over time. It’s also more prevalent among older people, and especially aging women, both groups that can experience weight gain as a result of the natural aging process. So, it’s common for hypothyroid individuals not to experience any significant weight loss, even after successful treatment.

The ATA states that, if all other symptoms of hypothyroidism, with the exception of weight gain, are resolved with the treatment of supplemental thyroid hormone, it’s less likely the weight gain is due solely to the thyroid. Once thyroid hormone levels return to a normal range, the ability to gain or lose weight is the same as in individuals who do not have thyroid problems.

In addition to unexplained weight gain and high TSH levels, other common signs of hypothyroidism are a swelling or enlargement in the neck, such as a goiter; hair loss; and an inability to get warm. If any or all of these symptoms are familiar to your situation, make an appointment with your primary care physician.

The Dignity Health Editorial Team manages the "Health Matters" blog with the mission of empowering our readers to be proactive about holistic wellness. We aim to provide clear and practical guidance around navigating health care through our unique lens of kindness, compassion, and humanity.

*This information is for educational purposes only and does not constitute health care advice. You should always seek the advice of your doctor or physician before making health care decisions.